Apparatus and method for providing ignition to a turbine engine

Abstract

A unipolar ignition of the invention provides a current waveform at the ignitor plug which initially rises relatively slowly, followed by a transition to a fast rising current which quickly peaks and thereafter slowly dissipates. Such a current waveform provides an initially hotter and longer lasting spark which does not harm the ignitor plug of the system or shorten its life expectancy. Neither does the spark create stress on the solid state circuitry which delivers the energy to the ignitor plug. To provide the foregoing spark and current characteristics, an inductor having a saturable core is in series with the ignitor plug, and it provides an initially high inductance which limits the rate of current rise at the plug as energy is transferred from an energy storage device to the plug. As the current through the inductor increases, its core begins to saturate and the effective inductance begins to decrease, allowing the current to rise more quickly. As energy is transferred to the ignitor plug. The increasing saturation, decreasing inductance and increasing current complement one another, causing the rate of current rise to increase quickly to a high value desirable for ignition. Related features of the invention provide for easy diagnostics of the spark and for timing an ignition sequence and providing a repetition rate which aids in a successful ignition.

We claim: 
     
       1. An ignition system for a gas turbine engine comprising in combination: a power supply;   a storage capacitor responsive to the power supply for storing energy at a voltage V;   an igniter plug responsive to the energy stored in the storage capacitor for generating a spark that ignites fuel in the turbine engine;   a solid state switch connected in series with the storage capacitor and the igniter plug for delivering the energy through the solid state switch and into the igniter plug in the form of a current that dwells in the at least several hundred amperes region for at least several microseconds in order to generate a spark that ignites fuel in the turbine engine;   a network interposed between the solid state switch and the igniter plug so as to form a series connection with the igniter plug and the solid state switch and, thereby, waveshape the voltage and current in order to efficiently ignite the fuel in the turbine engine;   a sensor responsive to the state of charge of the storage capacitor; and   a circuit responsive to the sensor for controlling the total energy stored by the storage capacitor.   
     
     
       2. The ignition system for a gas turbine engine as set forth in claim 1 wherein the circuit responsive to the sensor includes: means for generating a trigger signal; and   means for supplying the triggering signal to a control input of the solid state switch to render conductive the series connection and thereby discharge the energy stored in the storage capacitor through the solid state switch and the network and into the igniter plug.   
     
     
       3. The ignition system for a gas turbine engine as set forth in claim 1 wherein the network includes an inductor. 
     
     
       4. The ignition system for a gas turbine engine as set forth in claim 3 wherein the inductor is one winding of a transformer. 
     
     
       5. The ignition system for a gas turbine engine as set forth in claim 1 wherein a blocking diode is connected in parallel with the series connection of the network and igniter plug so that the discharging of the energy into the igniter plug occurs as a unipolar event. 
     
     
       6. The ignition system for a gas turbine engine as set forth in claim 1 wherein the series connection includes means for applying the energy to the igniter plug without a significant transformation of the value of the voltage V between the capacitor and the igniter plug. 
     
     
       7. The ignition system for a gas turbine engine as set forth in claim 1 wherein the circuit responsive to the sensor includes a device interposed between the power supply and the storage capacitor for metering delivery of the energy to the storage capacitor. 
     
     
       8. The ignition system for a gas turbine engine as set forth in claim 7 wherein the device is a DC-to-DC converter.